Lithographic plate graining machine clamp



Patented Dec. 28, 1948 LITKOGRAPHIC PLATE GRAINING MACHINE CLAMP MartinG. Dunn, Washington, D. C.

Application December 3, 1946, Serial No. 713,690

Claims.

This invention relates to improvements in lithographic plate grainingmachines, and. more particularly to hold-down devices for clampin theplates firmly and evenly upon the bottom of the grainer box or tub.

The general object of the invention is to provide a novel and improvedplate clamp for graining machines which may be quickly applied andreleased, which is resilient in action, and which is easy to manufactureand install while at the same time being of sturdy construction and notliable to get out of order or require frequent repair or replacement.

In its preferred embodiment, the invention contemplates the provision ofa spring pressed foot which, during operation of the machine, bearsresiliently upon the margins of the litho graphic plate being treated,either directly or through the intermediary of a. fiat hold-down strip.The spring pressure is released and the presser foot raised by means ofa novel manually actuated lifting cam, for replacement of the platesbetween operations.

Other objects, including the provision of presser feet of resilientmaterial and novel universal mountings for the presser 'feet, will beapparent from the following specification when read in connection withthe accompanying drawings in which certain embodiments of the inventionare illustrated by way of example.

In the drawings,

Figure 1 is a view in perspective of one end of the tub of a grainingmachine embodying the principles of the invention, the parts not beingdrawn to accurate scale but shown so as to best illustrate theconstruction and operation of the clamps;

Figure 2 is a fragmentary view in vertical section through one of thenovel clamps, and taken transversely of the supporting cross-bar; theclamp being in raised position;

Figure 3 is a similar view showing the clamp in applied position; and

Figure 4 is a fragmentary vertical sectional view through a presser footof alternative construction.

The grainer box or tub is indicated in the drawings by the referencenumeral and it will be understood by those skilled in the art that thetub 10 is mounted in a substantially horizontal position for rotary orgyratory movement in the horizontal plane. Means are also provided forloading the tub, after the lithographic plates are properly clampedtherein, with the steel balls or marbles and the wetted abrasivematerial, as is also well known in the art. The tub I0 is provided withan end wall I l, sidewalls l2, and a bottom wall [3 upon which issecured the rubber blanket IS, The margins of the rubber blanket l5 maybe extended a slight distance along the side walls H and I2 as at 16 andare adapted to be held in position by the strips or slats I1.

Lithographic plates 20 which are to be grained are laid in orderly rowsupon the blanket IS on the bottom of the tub, and are adapted to befirmly retained in flat position to be acted upon by the abrasive underthe influence of the rolling balls or marbles. These plates are of anyiamiliar type. whether made of zinc, copper, or aluminum, or whether newor used. The object of the graining process is to prepare clean grainedsurfaces on the plates for the reception of the lithographic image inthe process of lithoraphic or offset printing. In the case of thetreating of old plates, the object is to remove the old ima e from thesurface of the plate so that the plate may be used over and over again.

Although the hold-down clamp may be applied directly to the corners ormargins of the plates 20, it is preferred to cover the marginal edges ofthe plates with the hold-down strips 22 which are made of thin flexiblemetal and are preferably provided with bevelled or chamfered edges sothat the balls may roll freely across their surfaces as well as upon thesurfaces of the plates being treated.

The clamping arrangement comprises generally a series of cross bars 25which are adjustably secured at their ends to the inturned flanges 26 ofthe side walls [2 of the grainer tub. The flanges 26 are preferably cutaway adjacent the end of the tub so that the bars may be more readilyremoved when necessary. The cross bars 25 may be of any desiredcross-sectional configuration. being made either in one piece or builtup from simpler shapes such as fiat strips, angles, or channels.However, for the purpose of simplicity of illustration the cross bar inthe drawings is shown as being of X-section having a pair of verticalflanges 28 and a pair of hori zontal flanges 30. A transverse end plate21 is formed or welded adjacent the ends of the cross bar 25. andexteriorly of that end plate there are provided spaced flanges 28, thelower ones of which may comprise essentially continuations of thehorizontal flanges 30 of the cross bar. These spaced flanges are adaptedto slidingly'receive the flange 26 of the tub and the'bar 25is adaptedto receive one of the side flanges of the cross bar 25. The kerf 31 isinclined slightly to the horizontal so that it may be made slightlywider than the thickness of the flange to which it is applied and permita slight canting of the block 36 so that under pressure the block willassume a I substantially horizontal position.

The block 36 is drilled vertically to provide bore, and at its lower endagainst the pin 43,

which passes through the rod 40.

The rod is thus resiliently urged downwardly toward the bottom l3 of thetub Ill.

The lower end of the rod 45 is threaded as at 45 to adjustably'receivethe presser foot 46. This foot 46 comprises a rubber block, preferablyof cylindrical configuration, and provided with an opening or recesswithin whichis secured an internally threaded bushing ll to which therubber is secured as by vulcanizing. It will be readily understood thatthe presser foot may be rotated upon the shaft and disposed in differentpositions of adjustment, thus in eflect providing for the elongation ofthe rod 40, and accommodating it to the height of the layers or sheetmaterial to be clamped, and to compensate for any wear on the presserfoot. The presser foot 46 is adapted to bear resiliently upon thelithographic plates or upon the hold-down strips 22. The bearingpressure is made resilient both by means of .the coil spring 40 and theresilient nature of the pressure block 46. The resilient deformableblock 46 also permits the bottom surface of the presser foot to conformto the surface to which it is applied. 1

The release and lifting of the presser foot 4 is accomplished by meansof the hand lever 50 which is bifurcated as at 51 and provided with across pin 52 passing through the bifurcations and through the upper endof the rod 40, which is straddled by the bifurcations. The edge surfaces54 of the bifurcation 5! are provided with the proper cammingconfiguration to effect the lifting of the presser foot by swingingthe'lever 50 about the pin 52. The applied position of the clamp isshown in Figure 3, and it will be noted that in this postion the handle50 occupies a substantially horizontal position. In Figure 2 of thedrawings, the device is shown in its raised position wherein the handle50 has been moved through an angle of approximately 90 and the nose ofthe cam surface 5 1 bears upon the upper surface of the block 36.

In order to maintain the hand lever 50 in its proper position ofalignment when the presser foot is in applied position, there isprovided a keeper device consistng of a split pin 55' set in an openingin the upper wall of the block 36 and adapted to have its split andsomewhat resilient upper end received in the recess 56 drilled in thelower side of the lever 55. Within the broad purposes of the invention,this retaining means may assume a variety of different forms, the oneselected for illustration being merely typical of numerous retainingmeans which may be employed.

In Figure 4 of the drawings there is shown a modified form of presserfoot and rod in which the foot 46A is of metal and mounted for universalmovement upon the lower end of the rod 40A. An opening 41A is drilled inthe upper surface of the foot or block 46A, the bottom of the openingbeing preferably although not necessarily of. a conical or roughlyspherical shape as indicated at MB. The lower end of the rod 40A isprovided with an annular groove A within which a pin 46B is adapted tobe somewhat loosely received. The extreme lower end of the rod 40Acomprises'the head or enlargement'45B which is preferably provided witha flat conical or spherical lower surface conforming roughly to thesurface 413 of the opening 41A.

In this modification, the head 46A is provided with means afi'ordinguniversal rocking movement upon the end of the rod 40A whereby thebottom of the presser foot may find its proper bearing upon the strip 22or 'the lithographic plates 20, regardless of variations in the positionof the clamping device 35 on the cross bar 25.

In'orderto properly clamp the edges of the plates at the sides of thetub, similar clamps may be provided at intervals along the ledges orflanges 26 of the side walls l2 of the grainer tub.

It will be -seen that the present invention provides means which marks aconsiderable improvement over the old clamping devices, the clampingpressure of which has generally been attained by "screw clamps having.no resilientfeatures and beingvery time consuming in application andremoval. I

Various changes and modifications may be made in the embodimentsillustrated and, described herein without departing from the scope ofthe invention as defined in the following claims. p s

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is: n

1. In a lithographic plate graining machine, a grainer tub, a supportingmember extendin above and in spaced relation to the bottom of the tub,and at least one plate 'clamp'carried by said member, said clampcomprising a body portion secured to said member, a presser footdepending from said body portion; means for urging said foot resilientlydownwardly upon a plate resting upon the bottom of said tub, andmanually adjustable cam means'for raising said foot from operativeclamping position. I

2. In a lithographic plate graining machine, a grainer tub, a supportingmember extending above and in spaced relation to the bottom of the tub,and atleast one plate clamp carried by said member, said clampcomprising a body portion adapted to bear on said supporting member, asubstantially vertical rod guided vertically with respect to said bodyportion, a spring for urging said rod downwardly with'respect to saidbody portion, a presser foot on the lower end of said rod adapted tobear upon a plate on the bottom of said tub, a cam lever pivotedto theupper end of said rod and having a cam surface adapted to bear againstsaid body portion, whereby upon swinging of the lever the presser footis cammed upwardly and the pressure on the plate released.

3. In a lithographic plate graining machine, a grainer tub, a supportingmember extending above and in spaced relation to the bottom of the tub,and at least one plate clamp carried by said member, said clampcomprising a body portion adapted to bear on said supporting member, asubstantially vertical rod guided vertically through an opening in saidbody portion, a coil spring compressed between stop portions on saidbody portion and said rod for urging said rod downwardly with respect tosaid body portion, a presser foot on the lower end of said rod adaptedto bear upon a plate on the bottom of said tub, a manually actuated camlever pivoted to the upper end of said rod and havin a cam surfaceadapted to bear against the upper surface of said body portion, wherebyupon swinging of the lever the presser foot is cammed upwardly and thepressure on the plate released.

4. In a lithographic plate graining machine, a grainer tub, a supportingmember extending above and in spaced relation to the bottom of the tub,and at least one plate clamp carried by said member, said clampcomprising a body portion adapted to bear upon said supporting member, asubstantially vertical rod vertically movable relative to said bodyportion and having a presser foot on the lower end thereof, means urginsaid rod and foot downwardly toward the bottom of the tub, a leverfulcrumed on said body portion and pivotally connected with said rod,whereby swinging movement of the lever in a vertical plane toward andfrom said body portion causes the rod to be moved vertically withrelation to said body portion and said foot to be moved verticallyrelative to a plate on the bottom of said tub, against the influence ofsaid urging means, a guide pin extending from the surface of said bodyportion and adapted to wedgingly enter a recess in said lever as itmoves toward said body portion in approaching clamp applied position,whereby said lever is retained in said position until manually movedtherefrom.

5. In a lithographic plate graining machine, a graining tub, asupporting member extending above and in spaced re ation to the bottommem- Number her of the tub, and at least one plate clamp carrying saidmember, said clamp comprising a body portion adapted to bear upon saidsupporting member, the substantially vertical rod vertically androtatably movable relative to said body portion and having a presserfoot on the lower end thereof, means urging said rod and foot downwardlytoward the bottom of the tub, a cam lever pivotally mounted intermediateits length on the upper end of said rod and free to rotate therewithwhen not in clamping position, said lever having a camming end adaptedto bear against the surface of said body portion as a fulcrum, whereby aswinging movement of said cam lever toward and from said body portioncauses the rod to be moved vertically with relation to said body portionand said foot to be moved vertically relative to a plate on the bottomof the tub, against the influence of said urging means, a guide pinextending from the surface of said body portion and adapted to wedginglyenter a recess in said lever as it moves toward said body portion inapproaching clamp applied position, whereby said lever is retained insaid position until manually moved therefrom.

MARTIN GERALD DUNN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Williams July 1, 1884 Cornwall Sept. 19,1916 Lowe Apr. 9, 1918 Glaudel July 1, 1924 Zarkin Nov. 14, 1933 MetrickMay 29, 1934 Mandl Sept. 14, 1937 Mertes et al. Dec. 24, 1940 HarringtonMay 30, 1944 FOREIGN PATENTS Country Date Great Britain 1898 GermanyJan. 28, 1931 Number,

